1. Field of the Invention
The present invention relates to doors for wheeled vehicles, such as for sedans, vans, trucks, and other automobiles, and in particular to vertically sliding doors retractable in the automobile floor or roof.
2. Discussion of the Prior Art
Non-conventional door closures for automobiles have been experimented with for many years, showing up in non-production specialty cars and prototypes. Only recently, however, have practical vertically sliding doors been shown to be advantageous and feasible for existing standard automobile designs currently in high volume production. It is now known that vertically sliding doors may be designed into new cars without a large number of design constraints being imposed on the automobile designer. In fact, many of the difficult design constraints that now exist with conventional hinged automobile doors are eliminated by the use of vertically sliding doors. These inventive doors may be designed into existing body styles without any significant changes to the shape or appearance of the car. Both foreign and domestic automobile manufacturers are currently starting to explore the many economic advantages offered in safety, convenience, and ergonomics by this alternative to the standard hinged automobile door.
Two patents issued to the applicant, U.S. Pat. Nos. 4,801,172 and 4,940,282, explain the basic construction, features, and operation of the vertically sliding automobile door. In its preferred embodiment, the inventive door replaces conventional doors on a two or four door vehicle. The vertically sliding door has a window which retracts into the door in a standard fashion. However, the inventive door opens by retracting along an arcuate path under the floor rather than swinging outward from the vehicle as does a standard door. The inventive door and window are driven open and closed by one or more electric motors. When the door is driven into an elevated, closed position, structural keys on the door engage with receptacles in the chassis frame of the vehicle, and the door becomes a fully stressed structural member of the frame, providing a dramatic increase in the bending and torsional stiffness thereof. Preliminary analysis indicates an increase in bending stiffness of about nine times, and an increase in torsional stiffness of about two times compared with a chassis having conventional doors.
This structural integration of the door with the chassis frame provides numerous advantages. With this technology, vehicle frames can be designed with increased stiffness while being significantly lighter than their conventional frame counterparts. The same chassis frame can be used for different versions of a particular make of automobile. For instance, a convertible can have an identical lower structure as does a sedan, because the added stiffness provided by a roof is not relied upon by a vehicle design employing vertically sliding doors. Frontal and side impact resistance is also increased because vertically sliding doors provide a continuous structural frame around the passenger compartment, unlike conventional doors which may spring open or buckle inward in an accident.
To provide better aerodynamics, a more aesthetically pleasing profile, and an easier ingress and egress for passengers to the vehicle, today's vehicles are designed with higher tumblehome than before, top and bottom. Tumblehome is the amount a vehicle curves in towards the top or bottom from the widest point of the sides of the vehicle. An impediment to increasing lower tumblehome has traditionally been the large outer structural members of the car frame which run under the door sills. With the use of vertically sliding doors, these frame members can be reduced in size, moved toward the center of the vehicle, or preferably replaced altogether by the structural members of the new doors.
Other design constraints that are reduced or eliminated by vertically sliding doors include the constraints on the length of the doors. With conventional doors that swing out from the vehicle, the length of the door must be minimized to reduce its outward trajectory and cantilevered weight when opened. Vertically sliding doors can be lengthened up to the front and rear wheel wells, providing a wider door opening for easier ingress and egress to the front seats and also to the rear seats, if so equipped. A traditional four door car can utilize two long vertically sliding doors, providing access to the rear seats and eliminating the extra complexity, cost, and weight of the extra doors and door jambs. If four vertically sliding doors are preferred, automobile designers no longer are constrained with the need for providing roof columns between doors. Also, the constraint of the doors needing to be deeper than the height of the windows is removed with vertically sliding doors. Even with lower doors, and therefore taller windows, the windows can completely recess into the door, unlike many of today's car designs. This is because with vertically sliding doors, the windows may protrude through the bottom of the door when the windows are rolled down.
In addition to the increased tumblehome and door opening length described above, other features of the vertically sliding door make it easier to use than conventional car doors. The new doors are opened and closed automatically and are activated by a key chain remote control, a vehicle mounted keypad, or a traditional key and tumbler lock on the exterior of the car, and by electrical switches on the interior. A person with his or her arms full can enter the car simply by pushing a button. This inherent convenience of the vertical sliding door eliminates the awkward, unpredictable, and often dangerous opening and closing of doors while the vehicle is on a hill. Rather than dangerously swinging out into motor, bicycle or pedestrian traffic, the inventive door stows safely and conveniently under the vehicle with no obstruction to traffic. Because the side view mirrors stay stationary mounted to the side of the vehicle rather than swinging out with the doors, they can be used up until the moment the driver exits the car. Cars utilizing vertically sliding doors can be safely parked closer together or next to walls and other obstacles because there is no door to swing out and hit the adjacent object or get in the way of a person entering or exiting the car. A car also having a large amount of top and bottom tumblehome needs very little space next to it to allow easy ingress and egress.
Vertically sliding door technology also lends itself to the design of special vehicles for physically handicapped drivers. Because door operation is automatic, there is no problem in opening or closing the door for a person on crutches or in a wheelchair. The door does not swing out and limit the access of the door opening to a wheelchair, as do conventional doors. With the new doors, the unfolded wheelchair can even be loaded into the vehicle and secured in place of the standard driver's seat. An automatic lift can be used to lift the person and the wheelchair up and into the vehicle.
Other embodiments have been envisioned for the vertically sliding door concept. These configurations include vertically sliding side doors on vans, rear doors on vans and ambulances, tailgates on trucks, and door panels and or windows opening vertically and retracting above the roof of the vehicle in all of the above applications. Because vertically sliding door technology is relatively young, drawbacks exist in prior iterations and major improvements are continually being developed.
Structural members known as side intrusion beams are often used inside conventional doors to help protect passengers from injury during an impact to the side of the automobile. This type of beam traverses the door between the inner and outer door panels to inhibit the door from buckling inward in a side impact accident. However, to offer acceptable protection, these conventional beams must be of substantial cross section and therefore make the door heavier, impose space constraints on window and door mechanisms inside the door, and strongly influence overall door thickness. Vertically sliding doors are inherently stronger in a side impact because of their structural interlocking members, however side intrusion beams may still be beneficial across the center of the door to more fully protect passengers from an intrusion into the automobile during an accident.